The present invention relates to semiconductor fabrication, and in particular to methods for fabricating interconnect structures.
Reduction of integrated circuit size has resulted in levels of electrically conductive interconnects being placed closer together vertically, as well as reduction of the horizontal spacing between the electrically conductive interconnects, such as metal line. As a result, capacitance has increased between such conductive portions, resulting in loss of speed and increased crosstalk. One proposed approach to this problem is to replace the conventional silicon oxide (SiO2) dielectric material, having a dielectric constant (k) of about 4.0, with another insulation material having a lower dielectric constant to thereby lower capacitance.
Unfortunately, low-k dielectric materials have characteristics that make integration into existing integrated circuit structures and processes difficult. Compared to conventional silicon dioxide (SiO2), most low-k materials, due to the inherent structures thereof, typically present disadvantages of low mechanical strength, poor dimensional stability, poor temperature stability, high moisture absorption, permeation, poor adhesion, large thermal expansion coefficient, and unstable stress levels. Thus, the replacement of conventional silicon dioxide (SiO2) with low-k dielectric material in integrated circuit processes or structures becomes problematic, resulting in undesirable increases either in dielectric value of the used low-k material or in RC product (resistance x capacitance) of an integrated circuit structure such as an interconnect structure. Therefore, undesired speed losses and increased crosstalk issue may be happened to the integrated circuit structure.